Comparison of percentage fall in FVC at the provocative concentration of methacholine causing a 20% fall in FEV₁ between patients with asymptomatic bronchial hyperresponsiveness and mild asthma

Background: A significant proportion of individuals who have no symptoms of asthma or other respiratory diseases show bronchial hyperresponsiveness (BHR). BHR is usually assessed by measuring the provocative concentration of methacholine causing a 20% fall in FEV₁ (PC₂₀). The percentage fall in FVC at the PC₂₀ (ΔFVC) has been suggested to reflect maximal airway response and to be a more useful index of disease severity in asthma than PC₂₀. The aim of this study was to investigate whether asymptomatic BHR would differ from symptomatic BHR with regard to ΔFVC. Methods: Methacholine bronchial challenge tests were conducted in children with no past or current symptoms of asthma, allergic rhinitis, or other respiratory diseases, who were identified among siblings of children with asthma. Forty-three children with asymptomatic BHR (PC ₂₀ < 16 mg/mL) were recruited, and 43 children with mild asthma who were matched for age, sex, and PC₂₀ were selected (mild asthma group). The ΔFVC on methacholine concentration-response curves was retrospectively analyzed in the two groups. Results: There were no differences in the frequency of atopy, blood eosinophil counts, serum IgE levels, and spirometric values between the asymptomatic BHR and mild asthma groups. Mean (± SD) ΔFVC was significantly (p = 0.005) lower in the asymptomatic BHR group (14.5 ± 3.6%) than in the mild asthma group (16.9 ± 4.3%). Conclusions: Our results suggest that children with asymptomatic BHR have a lower level of maximal airway response than mild asthmatics with a similar degree of BHR. This may be a possible explanation for the lack of symptoms in subjects with asymptomatic BHR.